Smaller SC pulleys make more boost, and boost allows the engine to make more power. Be careful, though. If you go too small right away, the engine will knock, which will take away power and can even be harmful to your pistons.

The diameter of the OEM SC pulley is 3.8". Decreasing the diameter causes the blower to spin faster, creating higher than normal boost levels. It only takes a small change in pulley size to make a noticeable difference. Just a .1" diameter decrease will yield about 1 PSI increase in boost, which is enough to feel in your seat.

Aftermarket SC pulleys are now available in sizes ranging from 3.6" down to around 2". A word of caution: start bigger and work your way down. A 3.6" pulley can be used with little or no issues on a stock Riv, giving up to a 10 HP increase. A 3.5" pulley may give 15-20 HP and is probably fine if you run cooler plugs and t-stat, but scanning is still a good idea. Running the 3.4" size on a stock engine is not a good idea unless you scan and tune the PCM with a tuner or AFC device.

Average boost numbers on the stock 3.8" SC pulley will max around 6-8 PSI, depending on your car and the weather. With the 3.4", you'll see around 9-11 PSI. This extra air charge can add 25-30 HP to your engine's output, which is a very noticeable gain to say the least. Most of the extra power comes in the form of additional low-end torque, so you'll feel a lot of extra pull when launching the car. With this mod, wheel traction can begin to become an issue.

SC pulleys can be had for as low as $80 in the case of the press-on variety, but a modular system (MPS) is highly recommended. If you plan to modify further in the future, or if you want to experiment with different pulley sizes to dial in just the right boost for your car, an MPS lets you swap on a hub (like changing wheels) in only 5 minutes. You just loosen a few screws instead of having to pull and press on a new pulley. Modular systems go for between $100 and $130, but additional sizes are only $50-60, and many used pulleys can be found for less. Info on SC pulley installation is found here:

http://rivperformance.editboard.com/Supercharged-3800-Tech-c2/Series-II-FAQ-f19/How-do-I-remove-install-a-SC-Pulley-t511.htm

One of the things you'll notice with a smaller SC pulley is an even louder and higher pitched supercharger whine. Another thing you can expect is more KR. With more boost comes higher temps inside the cylinders, which can create knock. Also, smaller pulleys create much higher air flow rates than stock. The PCM will work to add more fuel, but with 3.5" or smaller, it's a good idea to scan after installation to confirm your air/fuel mixture is where it should be. If scanning indicates that KR has increased, you may need to reprogram the PCM, use an AFC to tune the air/fuel mix, add more modifications to fight knock, or use a larger SC pulley.

After adding a smaller SC pulley, you may be wondering if a smaller SC belt is needed. In most cases the answer is no, but it's a good idea to increase the diameter of the SC tensioner pulley to 3.5" ($20) in order to take up slack when running a 3.4" or smaller SC pulley. Additionally, going smaller than a 3.3" SC pulley requires using a 3.5" SC idler pulley as well. This is to ensure the SC does not rub against itself near the tensioner. Here are the rules:

-OEM SC belt works with OEM 3.8" SC pulley - keep tensioner and idler pulleys stock.

-OEM SC belt works with 3.6" and 3.5" SC pulleys - keep tensioner and idler pulleys stock.

-OEM SC belt works with 3.4" SC pulley - can keep stock tensioner pulley, or change to 3.5" - keep idler pulley stock.

-OEM SC belt works with 3.3" SC pulley - must change tensioner pulley to 3.5" - can keep stock idler pulley, or change to 3.5".

-OEM SC belt works with 3.2" SC pulley - must change both tensioner & idler pulleys to 3.5".

-OEM SC belt works with 3.1" SC pulley - must change both tensioner & idler pulleys to 3.5".

-using 3.0" or smaller SC pulleys will likely require a smaller SC belt size.

If your car has 85k miles or more, it is a good idea to change all of the idler and tensioner pulleys on both the accessory and SC belts. There are 5 pulleys total that run about $100 for all. For more info on pulleys/belts:

http://rivperformance.editboard.com/Supercharged-3800-Tech-c2/Series-II-FAQ-f19/-p4782.htm#4782

I am pretty well educated on the fact that a 3.4 inch pulley gets about 25-30 hp and a 3.25 inch pulley will get around 30+ hp... i have a cold air intake and 2.5 inch exhaust straight back from the cat.. no mufflers but i have two 3.5 inch tips they are 18 inches long... i am going to get a 160 degree or 180 degree thermostat?? which pulley shall i go with without gettin knock retard??

Welcome to the board! A good read through the FAQ will answer your questions in more detail.

A 3.25" SC pulley is out of the question for you with your current mods. Even a 3.4" is risky without a scanner to monior KR. The safest way to go would be a 3.6" or 3.5" SC pulley. Any smaller and you'll need to scan.

A 180º t-stat is best for daily driving.

i agree with Aaron, your exhaust mod doesnt really help relieve heat or back pressure, and if the CAI is one of the ebay ones, it's really a hot air intake which can cause more knock when there is heat soak. you can safely drop to a 3.5" IMO if you have a great running and clean engine and some supporting mods like colder plugs. make sure all the maint items have been taken care of before you get the mod bug
oh, and you should introduce yourself in the welcome page along with pics in the showroom. (so we can properly welcome you and see your ride! )
Matthew

thanks i have a home built CAI made out of 3.5 inch stainless steel which is wrapped in heat blocker i sort of went off of what someone else had done with PVC pipe... i will probably go with the 3.4 inch pulley and then see where i am at but yes i will first buy the 180 degree thermostat..... and to Mr. Riviera thats one nice Riv man i really wish i got a pearl white i instead got a black one......

i love the black riv's with some dark tint and chrome rims. dont forget to get some colder plugs along witht he 180 t-stat. and as Aaron mention'd read that FAQ it has a ton of good info.
congrats on the DIY CAI btw.

so yah i will probably be modding my riviera this summer i kno i said i was going to sell it WHICH I AM but i really wanna see the potential so i am going to install my FWI and get a 3.4 inch pulley with a new 180 t stat..... and then i am going to buy one of those AFC 2.0 gadgets to add more fuel <<<idk if thats what it does LMAO but yes then i will see if i can keep up to mr SRT-4

Keep in mind you need a scanner to use the AFC.

AHAHHAHAHA i really just wanna see the potential and actually the buyer of my car MY FRIEND will want mods

Without TUNING - not without SCANNING. You shouldn't be making too many mods or a pulley change without regular scanning. Know your engine, know the paramaters it runs at, know what it means when you have KR and why you have it.

PCM Tuning would take the place of an AFC. Scanning is used to TUNE the AFC. You are seriously changing the parameters from your MAF when you use an AFC. If you don't scan vigorously while TUNING your AFC you are going to do some damage.

You need to scan for MAF Hz, Front O2, MAP, IPW, KR at the very least. With all that info you can start making changes with an AFC.

why do scanners have to be so much $$$$$$$$$$$$$$$$$$$$

Keep your eyes open for a PC based autotap, that's the best. New they run $300. Mine sold used for $200. At that point you might as well spend $400 and get a tuner, that way you don't need an AFC!